You're right... these sort of rifles are just NOT made to be shot from the bench!
Lots of folks do it, and lots of folks are way better at it than I am... but they're NOT made for it. They're MADE for shooting standing.

Test from the bench if you must, but give your rifle what it desires; being shot from the hind legs.

Just my opinion, of course

Paul F.

As fallingblock said, a high front rest is required. I'll add to that by recommending a 2x6x6 block of wood under your rear bag. This gets the rifle butt up off the bench so your arm will fit in the buttplate. Keep adjusting and you'll get a comfortable position. The biggest aggrevation for me is when the rifle flops over and scares the crap out of me. Some people make a wide forestock to keep the rifle on the bags. Then change it for offhand. Some club rules may not allow that. I used to remove the palm rest when shooting bench. I found it makes no difference,so leave it on. some people remove the buttplate.  I remember when a rifle fell off a bench at a Coors match in Golden. Messed it up pretty bad. You'd thought someone had a heartattack and died. Then I was at a match where an old shooter did have a heartattack, the match went on, shooters looking over once in a while to see how the CPR was going. Go figger.     Joe

Some times I need to shoot my offhand rifles off a bench when testing new loads and components.

I have had so-so resuts with a very high front rest.  I added a long screw to a 2nd platform on one of the simple Protector rest. Resting the muzzle with the buttplate in my Shoulder and elbows on the bench it's possable to get some consistency.  If you look at the old pictures of Schuetzens being shot bench rest you will get the idea "Muzzle and elbow rest"

The weak point is the barrel to front bag  connection. It's possable to hold the butt end of the rifle about as well as off a bag.   Old timers used Sleds bolted onto the barrel to keep the rifle from Twisting on recoil and I suspect thats required .

Even with this high front rest I think the positon inconsistency hides group size changes. I can tell when something is peforming very poor but small changes and improvements are not possable to see.

Boats

Here is my bench method with traditionaly shaped stocks. Lets start at the front. Rest the barrel on the bag just in front of the forend. This will require that the rest be tall adding spacers to the bottom legs is one method that works well. Use a low rear bag that is still tall enough to keep the bottom prong of your butt plate off the bench. Place the butt on the bag at the place where the stock is the flatest. use a brick bag to keep your elbow up and your arm as stright as possible, recoil and the prong butt plate will twist the rifle when it is shot. Lastly the recoil must be contained with a non benchrest style stock. 

40 Rod

The biggest issue with shooting an offhand stocked rifle off the bench is the height you have to get to clear the lever and butt prongs.  In addition the thin almost blade-like schuetzen stocks and forends make the gun real "tippy" once you have it up on the rest and rear bag. This instability makes maintaining proper repetetive benchrest form a real challenge.  The ideal solution is of course a second set of wood designed for benchrest shooting.

For most rifles making a simple square sided and flatbottomed forend is a relatively simple matter, it is the butt that presents the biggest problem.

As an alternative to a dedicated butt for benchrest shooting, a number of the guys who shoot regularly at Etna Green have made grooved wooden adaptors that attach to the bottom of the butt that allow a wider flatter contact with the real bag.  it can be a simple as a hogged out section of 2x4 hardwood with an angled slot that the butt fits into with the bottom flat to the bench.  Then it is glas-bedded to the stock (with plenty of release agent) to give a good fit.

It can be attached with screws as some have done on a stock that is already buggered up. But if you have a nice offhand butt that you don't want to put holes in; it can be attached just as well by putting a little powdered rosin in the groove and then tapeing it in place with good quality packaging tape.  The forend on my 38-55 highwall has been taped to the barrel for a couple of years now--someday I really ought to finish it

I dig them slippers, I'm gonna get me some tomorrow.   Joe.

Ken tell me you didn't have those slippers on when we went out to eat with Tim. regards,ben.